Thin film forming apparatus cleaning method

ABSTRACT

A cleaning process for cleaning a thermal processing apparatus includes: a heating step of heating an interior of a reaction tube at 300° C., and a cleaning step of removing deposits deposited in the thermal processing apparatus. In the cleaning step, a cleaning gas containing fluorine gas, chlorine gas and nitrogen gas is supplied into the interior of the reaction tube heated at 300° C. to remove silicon nitride so to clean an interior of the thermal processing apparatus.

TECHNICAL FIELD

The present invention relates to a thin film deposition apparatuscleaning method and, more specifically, to a thin film depositionapparatus cleaning method, for removing deposits deposited on the innersurface of the thin film deposition apparatus during a process forforming a thin film on a workpiece, such as a semiconductor wafer.

BACKGROUND ART

A semiconductor device fabricating procedure includes a thin filmdeposition process, such as a CVD process (chemical vapor depositionprocess), for forming a thin film, such as a silicon dioxide film, asilicon nitride film or the like, on a workpiece, such as asemiconductor wafer. Such a thin film deposition process uses a thermalprocessing apparatus as shown in FIG. 15 to form a thin film on asemiconductor wafer by the following procedure.

A heater 53 heats a double-wall reaction tube 52 consisting of an innertube 52 a and an outer tube 52 b at a predetermined temperature. A waferboat 55 holding a plurality of semiconductor wafers 54 is loaded intothe reaction tube 52 (inner tube 52 a). Gases in the reaction tube 52are discharged through an exhaust port 56 to set the interior of thereaction tube 52 at a predetermined reduced pressure. After the interiorof the reaction tube 52 has been set at the predetermined reducedpressure, process gases are supplied through a gas supply pipe 57 intothe inner tube 52 a. The process gases undergo a thermal reaction, and areaction product produced by the thermal reaction deposits on thesurfaces of the semiconductor wafers 54 to form thin films on thesurfaces of the semiconductor wafers 54.

Waste gases produced by the thin film deposition process are dischargedoutside the thermal processing unit 51 through an exhaust pipe 58connected to the exhaust port 56. A trap and a scrubber and such, notshown, are placed in the exhaust pipe 58. The trap removes the reactionproduct and other substances contained in the waste gases to dischargethe waste gases from the thermal processing unit 51 after rendering thewaste gases harmless.

The reaction product produced by the thin film deposition processdeposits not only on (adheres not only to) the surfaces of thesemiconductor wafers 54, but also on (but also to) the inner surfaces ofthe thermal processing unit 51 including the inner surface of the innertube 52 a and the surfaces of jigs. If the thin film deposition processis continued in the thermal processing unit 51 with the reaction productadhering to the inside surfaces of the thermal processing unit 51, thereaction product will eventually come off and produce particles. Theparticles contaminate the semiconductor wafers 54, which reduces theyield of semiconductor devices which are manufactured using thesemiconductor wafers 54 contaminated with those particles.

To avoid such troubles, a cleaning process is carried out after the thinfilm deposition process has been repeated several times to clean thethermal processing unit 51. The cleaning process heats the reaction tube52 at a predetermined temperature by the heater 53, supplies a cleaninggas, such as a fluoride gas, into the heated reaction tube 52 to removeby etching the reaction product adhering to the inner surfaces of thethermal processing unit 51.

The fluoride gas for such a purpose is a perfluorocompound, such as CF₄,C₂F₆, NF₃ or SF₆. Generally, the perfluorocompond has a long life. Forexample, CF₄ lasts 50,000 years or longer. The emission of theperfluorocompound into the atmosphere causes global warming. Since thereis the possibility that the use of the fluoride gas as a cleaning gasnegatively affects the global environment, studies have been made to usea cleaning gas other than the perfluorocompound, such as fluorine gas(F₂).

The interior of the reaction tube 52 must be heated at the predeterminedtemperature to make the cleaning gas etch the reaction product at adesired etch rate to remove the reaction product deposited on the innersurfaces of the thermal processing unit 51. The interior of the reactiontube 52 needs to be heated at a high temperature of, for example, 400°C., to etch the deposited reaction product at a desired etch rate usingfluorine gas as a cleaning gas.

If the interior of the reaction tube 52 is heated at such a hightemperature of 400° C., the reaction tube 52 formed of quartz and thejigs formed of silicon carbide (SiC) are etched at etch rates higherthan that at which the reaction product is etched, and reaction productselectivity, i.e., the ratio between etch rates for the reaction productand the material, decreases. Consequently, the reaction tube 52 formedof quartz, and the jigs formed of SiC are deteriorated when the reactiondeposit is removed.

DISCLOSURE OF THE INVENTION

The present invention has been made in view of the foregoing problemsand it is therefore an object of the present invention to provide a thinfilm deposition apparatus cleaning method capable of removing depositsdeposited inside the thin film deposition apparatus, suppressing thedeterioration of a reaction vessel and jigs.

Another object of the present invention is to provide a thin filmdeposition apparatus cleaning method capable of etching depositsdeposited inside the thin film deposition apparatus at a high etch rate.

A third object of the present invention to provide a thin filmdeposition apparatus cleaning method capable of removing depositsdeposited inside the thin film deposition apparatus with the interior ofa reaction vessel heated at a low temperature.

According to the present invention, a thin film deposition apparatuscleaning method of cleaning a thin film deposition apparatus by removingdeposits adhering to an inner surfaces of the thin film depositionapparatus after depositing thin films on workpieces by supplying aprocess gas into a reaction vessel included in the thin film depositionapparatus comprises the steps of: heating an interior of the reactionvessel at a predetermined temperature; and cleaning an interior of thethin film deposition apparatus by supplying a cleaning gas containingfluorine gas and an additive gas capable of promoting the activation ofthe fluorine gas into the reaction vessel heated at the predeterminedtemperature, heating the cleaning gas at a predetermined temperature toactivate the fluorine gas contained in the cleaning gas, and removingthe deposits with the activated fluorine gas.

According to the present invention, the cleaning gas is supplied intothe reaction vessel heated at the predetermined temperature, thecleaning gas supplied into the reaction vessel is heated at thepredetermined temperature, and thereby the fluorine gas contained in thecleaning gas is activated. Since the cleaning gas contains the additivegas capable of activating the fluorine gas, the activation of thefluorine gas is promoted. Since the activation of the fluorine gas isthus promoted, the deposits adhering to the interior of the thin filmdeposition apparatus can be etched at a high etch rate. The etch ratefor the deposits is high and hence the temperature in the reactionvessel may be low. Thus, the temperature in the reaction vessel may below during the removal of deposits deposited in the thin film depositionapparatus.

According to the thin film deposition apparatus cleaning method of thepresent invention, the deposits are removed and the interior of the thinfilm deposition apparatus is cleaned by supplying the cleaning gascontaining fluorine gas and the additive gas capable of promoting theactivation of the fluorine gas and of increasing the etch rate for thedeposits without decreasing selectivity, i.e., the ratio of the etchrate for the deposit to that for the materials forming the internalmembers of the thin film deposition apparatus, into the reaction vesselin the cleaning step.

According to the present invention, the cleaning gas supplied into thereaction vessel etches the deposits at a high etch rate withoutdecreasing selectivity with respect to the materials forming theinternal members of the thin film deposition apparatus owing to theagency of the additive gas. Consequently, the deposits deposited in thethin film deposition apparatus can be removed, suppressing thedeterioration of the internal members of the thin film depositionapparatus, such as the reaction vessel and the jigs.

According to the thin film deposition apparatus cleaning method of thepresent invention, chlorine gas, hydrogen fluoride gas, ammonia gas orhydrogen gas is used as an additive gas.

According to the thin film deposition apparatus cleaning method of thepresent invention the deposits to are removed to clean the interior ofthe thin film deposition apparatus by supplying a cleaning gascontaining fluorine gas and chlorine gas into the reaction vessel heatedat the predetermined temperature in the cleaning step.

According to the present invention, the cleaning gas contains fluorinegas and chlorine gas, and etches the deposits at a high etch ratewithout decreasing selectivity with respect to the materials forming theinternal members of the thin film deposition apparatus. Consequently,the deposits deposited in the thin film deposition apparatus can beremoved, suppressing the deterioration of the internal members of thethin film deposition apparatus, such as the reaction vessel and thejigs.

According to the thin film deposition apparatus cleaning method of thepresent invention, the deposits are removed to clean the interior of thethin film deposition apparatus by supplying a cleaning gas containingfluorine gas and hydrogen fluoride gas into the reaction vessel heatedat a predetermined temperature in the cleaning step.

According to the present invention, the cleaning gas contains fluorinegas and hydrogen fluoride gas, and the deposits are etched at a highetch rate without decreasing selectivity with respect to the materialsforming the internal members of the thin film deposition apparatus.Consequently, the deposits deposited in the thin film depositionapparatus are removed, suppressing the deterioration of the reactionvessel and the jigs.

According to the thin film deposition apparatus cleaning method of thepresent invention, the cleaning gas containing fluorine gas and hydrogenfluoride gas supplied such that the flow rate ratio between fluorine gasis supplied and hydrogen fluoride gas is in the range of 1:3 to 3:1.

When fluorine gas and hydrogen fluoride gas of the cleaning gas issupplied such that the flow rate ratio between fluorine gas and hydrogenfluoride gas is in the range of 1:3 to 1:1, the etch rate for thedeposits deposited in the thin film deposition apparatus, andselectivity with respect to the materials forming the internal membersof the thin film deposition apparatus are high.

According to the thin film deposition apparatus cleaning method of thepresent invention, the cleaning gas containing fluorine gas and hydrogenfluoride gas is supplied such that the flow rate ratio between fluorinegas are supplied and hydrogen fluoride gas is 1:1.

In this case, selectivity with respect to quartz generally used forforming the internal members of thin film deposition apparatuses ishigh.

According to the thin film deposition apparatus cleaning method of thepresent invention, fluorine gas and hydrogen fluoride gas are suppliedrespectively at flow rates not lower than 2 l/min.

In this case, the deposits deposited in the thin film depositionapparatus is etched at a high etch rate, and selectivity with respect toquartz is high.

According to the thin film deposition apparatus cleaning method of thepresent invention, the deposits are removed to clean the interior of thethin film deposition apparatus by supplying a cleaning gas containingfluorine gas and ammonia gas into a reaction vessel heated at apredetermined temperature.

According to the present invention, the cleaning gas containing fluorinegas and ammonia gas etches the deposits at a high etch rate withoutdecreasing selectivity with respect to the materials forming theinternal members of the thin film deposition apparatus. Consequently,the deposits deposited in the thin film deposition apparatus areremoved, suppressing the deterioration of the reaction vessel and thejigs.

According to the thin film deposition apparatus cleaning method of thepresent invention, the cleaning gas containing fluorine gas and ammoniagas is supplied such that the flow rate ratio between fluorine gas andammonia gas is in the range of 2:1 to 10:1.

In this case, the deposits deposited in the thin film depositionapparatus are etched at a high etch rate, and selectivity with respectto the materials forming the internal members of the thin filmdeposition apparatus is high.

According to the thin film deposition apparatus cleaning method of thepresent invention, the deposits are removed to clean the interior of thethin film deposition apparatus by supplying a cleaning gas containingfluorine gas and hydrogen gas is supplied into the reaction vesselheated at a predetermined temperature in the cleaning step.

According to the present invention, the cleaning gas containing fluorinegas and hydrogen gas etches the deposits at a high etch rate withoutdecreasing selectivity with respect to the materials forming theinternal members of the thin film deposition apparatus. Consequently,the deposits deposited in the thin film deposition apparatus areremoved, suppressing the deterioration of the reaction vessel and thejigs.

According to the thin film deposition apparatus cleaning method of thepresent invention, the cleaning gas containing fluorine gas and hydrogengas is supplied such that the flow rate ratio between fluorine gas andhydrogen gas is in the range of 5:1 to 5:3.

In this case, the deposits deposited in the thin film depositionapparatus are etched at a high etch rate, and selectivity with respectto the materials forming the internal members of the thin filmdeposition apparatus is high. Silicon nitride can be etched at a highetch rate even if the flow rate of hydrogen gas is not controlledprecisely. Consequently, the flow rate of hydrogen gas can easily becontrolled.

According to the thin film deposition apparatus cleaning method of thepresent invention, the cleaning gas containing fluorine gas and hydrogengas is supplied such that the flow rate ratio between fluorine gas andhydrogen gas is 5:3.

In this case, the etch rate for quartz generally used for formingreaction vessels is low, so that the deposits deposited in the thin filmdeposition apparatus can be removed, suppressing the deterioration ofthe reaction vessel:

In the thin film deposition apparatus cleaning method according to thepresent invention, the materials forming the internal members of thethin film deposition apparatus include at least either quartz or siliconcarbide.

According to the thin film deposition apparatus cleaning method of thepresent invention, the interior of the reaction vessel is heated at atemperature below 400° C. in the heating step.

According to the thin film deposition apparatus cleaning method of thepresent invention, the interior of the reaction vessel is heated at atemperature in the range of 250° C. to 380° C. in the heating step.

By heating the interior of the reaction vessel at temperatures in theaforesaid range, the deposits can be etched at a high etch rate, whilesuppressing the deterioration of the reaction vessel and the jigs.

According to the thin film deposition apparatus cleaning method of thepresent invention, the cleaning gas is diluted with a diluent gas toproduce a diluted cleaning gas, and the diluted cleaning gas is suppliedinto the reaction vessel.

According to the thin film deposition apparatus cleaning method of thepresent invention, uses an inert gas is used as the diluent gas.

By using the diluted cleaning gas, a cleaning time can be easily set inthe cleaning step.

In the thin film deposition apparatus cleaning method according to thepresent invention, silicon nitride films are formed on the workpieces,and in the cleaning step silicon nitride deposited in the thin filmdeposition apparatus is removed, when depositing the silicon nitridefilms on the workpieces with the cleaning gas.

According to the present invention, a thin film deposition apparatuscleaning method of cleaning a thin film deposition apparatus by removingdeposits adhering to the inner surface of an exhaust pipe after formingthin films on workpieces by supplying a process gas in a reaction vesselincluded in the thin film deposition apparatus and discharging gasesfrom the reaction vessel in to the exhaust pipe comprises the steps of:heating an interior of the exhaust pipe at a predetermined temperature;and cleaning an interior of the exhaust pipe by supplying a cleaning gascontaining fluorine gas and an additive gas capable of promoting theactivation of the fluorine gas into the exhaust pipe heated at thepredetermined temperature in the heating step, heating the cleaning gasat a predetermined temperature to activate the fluorine gas contained inthe cleaning gas, and removing the deposits with the activated fluorinegas.

According to the thin film deposition apparatus cleaning method of thepresent invention, the cleaning gas is supplied through the reactionvessel into the exhaust pipe.

According to the thin film deposition apparatus cleaning method of thepresent invention, the cleaning gas is supplied through an inlet portformed in the exhaust pipe into the exhaust pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a thermal processing apparatus to which athermal film deposition apparatus cleaning method in a preferredembodiment according to the present invention is applied;

FIG. 2 is a diagram of a recipe of assistance in explaining the thermalfilm deposition apparatus cleaning method in the preferred embodimentaccording to the present invention;

FIG. 3 is a table of cleaning conditions and results of execution of thethermal film deposition apparatus cleaning method using chlorine gas asan additive gas;

FIG. 4 is a graph showing etch rates at which materials are etched byusing cleaning gases containing chlorine gas as an additive gas;

FIG. 5 is a graph showing selectivities with respect to materials whencleaning gases containing chlorine gas as an additive gas are used;

FIG. 6 is a table of cleaning conditions and results of execution of thethermal film deposition apparatus cleaning method using hydrogenfluoride gas as an additive gas;

FIG. 7 is a graph showing etch rates at which materials are etched byusing cleaning gases containing hydrogen fluoride gas as an additivegas;

FIG. 8 is a graph showing selectivities with respect to materials whencleaning gases containing hydrogen fluoride gas as an additive gas areused;

FIG. 9 is a table of cleaning conditions and results of execution of thethermal film deposition apparatus cleaning method using ammonia gas asan additive gas;

FIG. 10 is a graph showing etch rates at which materials are etched byusing cleaning gases containing ammonia gas as an additive gas;

FIG. 11 is a graph showing selectivities with respect to materials whencleaning gases containing ammonia gas as an additive gas are used;

FIG. 12 is a table of cleaning conditions and results of execution ofthe thermal film deposition apparatus cleaning method using hydrogen gasas an additive gas;

FIG. 13 is a graph showing etch rates at which materials are etched byusing cleaning gases containing hydrogen gas as an additive gas;

FIG. 14 is a graph showing selectivities with respect to materials whencleaning gases containing hydrogen gas as an additive gas are used; and

FIG. 15 is a schematic view of a thermal processing apparatus ofassistance in explaining the adhesion of reaction products to thethermal processing apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

A thin film deposition apparatus cleaning method in a preferredembodiment according to the present invention will be described asapplied to cleaning a batch-furnace vertical thermal processingapparatus (thin film deposition apparatus) 1 shown in FIG. 1. Thethermal processing apparatus 1 (thin film deposition apparatus) 1 towhich this embodiment is applied will be described.

Referring to FIG. 1, the thermal processing apparatus 1 has asubstantially cylindrical reaction tube (reaction vessel) 2 in avertical position, and an exhaust pipe 17 for carrying gases dischargedfrom the reaction tube 2. The reaction tube (reaction vessel) 2 is adouble-wall structure consisting of an inner tube 3, and a topped outertube 4 covering the inner tube 3 so that an annular space is definedbetween the inner tube 3 and the outer tube 4. The inner tube 3 and theouter tube 4 are formed of a heat-resistant material, such as quartz.

The outer tube 4 is mounted on a manifold 5 formed of a stainless steel(SUS). The manifold 5 is joined airtightly to the lower end of the outertube 4. The inner tube 3 is supported on a support ring 6 formedintegrally with the manifold 5 so as to protrude from the innercircumference of the manifold 5.

A cover 7 is disposed under the manifold 5. A boat elevator 8 moves thecover 7 vertically. The boat elevator 8 raises the cover 7 to close thebottom of the manifold 5.

A wafer boat 9 formed of, for example, quartz is mounted on the cover 7.The wafer boat 9 is capable of holding a plurality of workpieces, forexample, semiconductor wafers 10 at predetermined spacing in a verticalarrangement.

A heat-insulating member 11 is provided to surround the reaction tube 2.A heater 12 having a resistive heating element is attached to the innersurface of the side wall of the heat-insulating member 11.

A plurality of process gas supply pipes 13 are connected to the sidewall of the manifold 5. Only one of the process gas supply pipes 13 isshown in FIG. 1. The process gas supply pipes 13 is open into the innertube 3. For example, the process gas supply pipes 13 are connected toparts, below the support ring 6 (below the inner tube 3), of the sidewall of the manifold 5. Process gases are introduced through the processgas supply pipes 13 into the inner tube 3 so as to be delivered to thesemiconductor wafers 10.

A cleaning gas supply pipe 14 is connected to the side wall of themanifold 5 so as to open into the inner tube 3. A cleaning gas isintroduced through the cleaning gas supply pipe 14 into the inner tube3.

An exhaust port 15 is formed in a part, above the support ring 6, of theside wall of the manifold 5 so as to be open into the annular spacebetween the inner tube 3 and the outer tube 4 of the reaction tube 2.Waste gases produced inside the inner tube 3 are discharged through theannular space between the inner tube 3 and the outer tube 4, and theexhaust port 15. A purge gas supply pipe 16 is connected to a part,below the exhaust port 15, of the side wall of the manifold 15 to supplynitrogen gas as a purge gas into the reaction tube 2.

The exhaust pipe 17 is connected airtightly to the exhaust port 15. Theexhaust pipe 17 is provided with a valve 18, and a vacuum pump 19 belowthe valve 18. The opening of the valve 18 is adjusted to adjust the flowof gases through the exhaust pipe 17 to maintain the interior of thereaction tube 2 at a predetermined pressure. The vacuum pump 19discharges gases from the reaction tube 2 through the exhaust pipe 17and adjusts the pressure in the reaction tube 2.

A trap, a scrubber and such, not shown, are placed in the exhaust pipe17 to discharge the waste gases discharged from the reaction tube 2 fromthe thermal processing apparatus 1 after rendering the waste gasesharmless.

A controller 20 is connected to the boat elevator 8, the heater 12, theprocess gas supply pipes 13, the cleaning gas supply pipes 14, the purgegas supply pipe 16, the valve 18 and the vacuum pump 19. The controller20 includes a microprocessor and a process controller. The controller 20measures the temperatures and pressures of controlled parts of thethermal processing apparatus 1, gives control signals produced on thebasis of measured data to the controlled parts to control the controlledparts of the thermal processing apparatus 1 according to a recipe(sequence diagram) shown in FIG. 2.

A thin film deposition apparatus cleaning method in a preferredembodiment according to the present invention will be described asapplied to cleaning the thermal processing apparatus 1. The thin filmdeposition apparatus cleaning method will be described as applied toremoving silicon nitride deposited in the thermal processing apparatus 1during a film deposition process for depositing silicon nitride films onsemiconductor wafers 10 to clean the interior of the thermal processingapparatus 1, particularly, the interior of the reaction tube 2 withreference to the recipe shown in FIG. 2. In the following description,it is assumed that the controller 20 controls the operations of thecomponents of the thermal processing apparatus 1.

First the film deposition process will be described.

The boat elevator 8 lowers the cover 7, and the wafer boat 9 holdingsemiconductor wafers 10 is mounted on the cover 7. A predeterminedamount of nitrogen gas is supplied through the purge gas supply pipe 16into the reaction tube 2, the boat elevator 8 raises the cover 7 to loadthe wafer boat 9 into the reaction tube 2. Thus, the semiconductorwafers 10 are contained in the inner tube 3 of the reaction tube 2, andthe reaction tube 2 is sealed (Loading step),

After the reaction tube 2 has been sealed, a predetermined nitrogen gasis supplied through the purge gas supply pipe 16 into the reaction tube2, the opening of the valve 18 is controlled, and the vacuum pump 19 isactuated to discharge gases from the reaction tube 2 to start evacuatingthe reaction tube 2. The reaction tube 2 is evacuated until the pressurein the reaction tube 2 decreases to a predetermined pressure of, forexample, 65.5 Pa (0.5 torr). In the meantime, the heater 12 heats theinterior of the reaction tube 2 at, for example, 600° C. Thepressure-decreasing operation and the heating operation are continueduntil the interior of the reaction tube 2 is stabilized at thepredetermined pressure and the predetermined temperature (Stabilizingstep).

After the interior of the reaction tube 2 has been stabilized at thepredetermined pressure and the predetermined temperature, the supply ofnitrogen gas through the purge gas supply pipe 16 is stopped. Then,hexachlorodisilane (Si₂Cl₆) and ammonia (NH₃) are supplied atpredetermined supply rates, for example, 0.1 l/min and 1 l/m,respectively, through the process gas supply pipes 13 into the innertube 3.

The hexachlorodisilane and ammonia introduced into the inner tube 3 arecaused by heat in the reaction tube 2 to undergo a thermal decompositionreaction. Consequently, silicon nitride (Si₃N₄) deposits on the surfacesof the semiconductor wafers 10 in silicon nitride films (Si₃N₄ films)(Film deposition step).

After the silicon nitride films of a predetermined thickness have beenformed on the surfaces of the semiconductor wafers 10, the supply ofhexachlorodisilane and ammonia through the process gas supply pipes 13is stopped. Then, the vacuum pump 19 is actuated, the opening of thevalve 18 is controlled and, at the same time, a predetermined amount ofnitrogen gas is supplied through the purge gas supply pipe 16 todischarge the gases from the reaction tube 2 through the exhaust pipe 17(Purging step). Preferably, the gas discharging operation and thenitrogen gas supply operation to discharge gases from the reaction tube2 are repeated several times to ensure that all the gases are dischargedcompletely from the reaction tube 2.

Then, a predetermined amount of nitrogen gas is supplied through thepurge gas supply pipe 16 into the reaction tube 2 to set the interior ofthe reaction tube at normal pressure. Subsequently, the boat elevator 8lowers the cover 7 to unload the wafer boat holding the semiconductorwafers 10 from the reaction tube 2 (Unloading step).

Silicon nitride produced by the film deposition process deposits on(adhere to) not only the surfaces of semiconductor wafers 10, but alsoon the inner surfaces of the reaction tube 2, such as the inner surfaceof the inner tube 3 formed of quartz, and on jigs formed of SiC as thefilm deposition process is repeated several times. A cleaning processfor removing silicon nitride deposited in the thermal processingapparatus 1 is performed after the film deposition process has beenrepeated a predetermined number of times. In the cleaning processsupplies a cleaning gas containing fluorine gas (F₂), an additive gasfor promoting the activation of fluorine gas, and nitrogen gas (N₂) as adiluent gas is supplied into the reaction tube 2 of the thermalprocessing apparatus 1. The cleaning process for cleaning the thermalprocessing apparatus 1 will be described.

After a predetermined amount of nitrogen gas has been supplied throughthe purge gas supply pipe 16 into the reaction tube 2, a wafer boat 9not holding any semiconductor wafers is mounted on the cover 7. Then theboat elevator 8 raises the cover 7 so that the reaction tube 2 issealed. Subsequently, the supply of nitrogen gas through the purge gassupply pipe 16 is stopped, gases are discharged from the reaction tube 2to maintain the interior of the reaction tube 2 at a predeterminedpressure of, for example, 53,200 Pa (400 torr), and the heater 12 heatsthe reaction tube 2 to heat the interior of the reaction tube 2 at apredetermined temperature of, for example, 300° C. (Heating step).

Then, a predetermined amount of the cleaning gas is supplied through thecleaning gas supply pipe 14 into the inner tube 3. The cleaning gas isheated in the inner tube 3. Consequently, the fluorine gas contained inthe cleaning gas is activated and many reactive free atoms are produced.The additive gas contained in the cleaning gas promotes the activationof the fluorine gas. As the cleaning gas containing the activatedfluorine gas flows from the interior of the inner tube 3 through theannular space formed between the inner tube 3 and the outer tube 4 intothe exhaust pipe 17, the cleaning gas etches silicon nitride depositedon the inner and outer surfaces of the inner tube 3, the inner surfaceof the outer tube 4, the inner surface of the exhaust pipe 17, the boat9, and the jigs including a heat-insulating tube and placed in thethermal processing apparatus 1. Thus, the silicon nitride deposited inthe thermal processing apparatus 1 is removed (Cleaning step).

After the silicon nitride deposited in the thermal processing apparatushas been removed, the supply of the cleaning gas through the cleaninggas supply pipe 14 is stopped. Then, the valve 18 is opened properly,the vacuum pump 19 is actuated to discharge gases contained in thereaction tube 2 and, at the same time, nitrogen gas is supplied throughthe purge gas supply pipe 16 into the reaction tube 2 to purge the gasesfrom the reaction tube 2 into the exhaust pipe 17 (Purging step).Preferably, the gas discharging operation and the nitrogen gas supplyoperation are repeated several times to ensure that all the gases aredischarged completely from the reaction tube 2.

Then, the valve 18 is closed, a predetermined amount of nitrogen gas issupplied through the purge gas supply pipe 16 to set the interior of thereaction tube 2 at normal pressure (Normal pressure setting step). Then,the boat elevator 8 lowers the cover 7, and a wafer boat 9 holdingsemiconductor wafers 10 is mounted on the cover 7. Then, the filmdeposition process for depositing silicon nitride films on thesemiconductor wafers 10 is started in the thus cleaned thermalprocessing apparatus 1.

The etch rates at which the cleaning gas etches materials, andselectivities (etching selectivities) of the cleaning gases with respectto materials were measured to verify the effect of the embodiment of thepresent invention. Each cleaning gas contained fluorine gas, an additivegas, and a diluent gas, such as nitrogen gas. The additive gas thatpromotes the activation of fluorine gas was chlorine gas (Cl₂), hydrogenfluoride gas (HF), ammonia gas (NH₃) or hydrogen gas (H₂). A thin filmdeposition apparatus cleaning method in Example 1 used chlorine gas,thin film deposition apparatus cleaning methods in Examples 2 to 5 usedhydrogen fluoride gas, thin film deposition apparatus cleaning methodsin Examples 6 to 8 used ammonia gas, and thin film deposition apparatuscleaning methods in Examples 9 to 11 used hydrogen gas as additivegases, respectively.

Three kinds of specimens, namely, specimens formed of quartz, specimensformed of SiC, specimens prepared by depositing 3 μm thick siliconnitride films on quartz chips, were subjected to cleaning experiments.The specimens were held on a wafer boat 9, the wafer boat 9 was placedin the reaction tube 2, and the cleaning gases were supplied into thereaction tube 2 to clean the specimens. Then, the specimens thus cleanedwere measured to determine etch rates and selectivities for thespecimens. Etch rates were calculated from weight changes of thespecimens caused by the cleaning process. The interior of the reactiontube 2 was heated at 300° C., and the pressure in the reaction tube 2was adjusted to 53,200 Pa (400 torr) for the cleaning experiments.

Selectivity (etching selectivity) is an etch rate ratio between thematerials of the specimens. For example, silicon nitride selectivitywith respect to quartz is the ratio of silicon nitride etch rate toquartz etch rate. The etch rates for specimens were determined by thetypes and supply rate of additive gases, and the supply rate of thediluent gas.

EXAMPLE 1

In a thin film deposition apparatus cleaning method in Example 1,fluorine gas, chlorine gas and nitrogen gas are supplied at 2 l/min,0.35 l/min and 8 l/min, respectively, that is to say, a cleaning gas issupplied at 10.35 l/min through the cleaning gas supply pipe 14 into thereaction tube 2. FIGS. 3 to 5 show measured etch rates, and measuredSi₃N₄ selectivities when the specimens were cleaned by the thin filmdeposition apparatus cleaning method in Example 1 using chlorine gas asan additive gas, together with those in a thin film deposition apparatuscleaning method in Comparative example 1 using a cleaning gas containingfluorine gas and nitrogen gas and not containing chlorine gas, and thosein a thin film deposition apparatus cleaning method in Comparativeexample 2 using a cleaning gas containing fluorine gas and nitrogen gasand heating the interior of the reaction tube 2 at 400° C.

It is known from the comparative examination of data on the results ofcleaning by Example 1 and Comparative example 1 shown in FIGS. 3 and 4that the cleaning gas containing chlorine gas is capable of etchingsilicon nitride at a high etch rate without heating the reaction tube 2at an elevated temperature. It is considered that the chlorine gascontained in the cleaning gas promoted the activation of the cleaninggas.

It is known from the comparative examination of data on the results ofcleaning by Example 1 and Comparative example 1 shown in FIGS. 3 and 4that Si₃N₄ selectivities with respect to quartz and SiC are high whenthe cleaning gas containing chlorine gas is used because the rates ofincreases in etch rates for quartz and SiC are smaller than that ofincrease in the etch rate for Si₃N₄. Thus, Si₃N₄ selectivity does notdecrease when the cleaning gas containing chlorine gas is used, andsilicon nitride adhering to the inner surfaces of the reaction tube 2can be removed without deteriorating the reaction tube 2 and the jigs byusing the cleaning gas containing chlorine gas. Particularly, the Si₃N₄selectivity with respect to SiC achieved by Example 1 is about fourtimes that achieved by Comparative example 1 and is about eight timesthat achieved by Comparative example 2. Thus, Example 1 is effective insuppressing the deterioration of jigs formed of SiC.

Although the silicon nitride etch rate in Comparative example 2 thatheats the reaction tube 2 at 400° C. is high as compared with those inExample 1 and Comparative example 1, in Comparative example 2 quartz andSiC are etched at high etch rates. Consequently, as shown in FIGS. 3 and4, the Si₃N₄ selectivities with respect to quartz and SiC are low. Thuswhen silicon nitride deposited in the thermal processing apparatus 1 isremoved in Comparative example 2, the reaction tube 2 of quartz and thejigs of SiC inevitably deteriorate.

It is proved from the above experiments that it is preferable to heatthe reaction tube 2 at a low temperature of 300° C. lower than 400° C.and to use a cleaning gas containing chlorine gas to etch siliconnitride at a high etch rate without decreasing Si₃N₄ selectivity(maintaining Si₃N₄ selectivity at a high level).

It is preferable to heat the interior of the reaction tube 2 at atemperature below 400° C. for the cleaning step, because it is possiblethat the reaction vessel 2 of quartz and the jigs of SiC aredeteriorated when the interior of the reaction tube 2 is heated attemperatures above 400° C. More preferably, the temperature in thereaction tube 2 for the cleaning step is in the range of 250° C. to 380°C. The cleaning gas is not satisfactorily activated, silicon nitrideetch rate is low and silicon nitride cannot be etched at a desirableetch rate, if the temperature in the reaction tube 2 is below 250° C.Quartz and SiC are etched at high etch rates and Si₃N₄ selectivity islow, if the temperature in the reaction tube 2 is higher than 380° C.

The cleaning gas containing chlorine gas is capable of etching siliconnitride at a high etch rate, and hence the temperature in the reactiontube 2 in the cleaning step can further be lowered when the cleaning gascontaining chlorine gas is used. The deterioration of the reaction tube2 and the jigs can be suppressed by heating the interior of the reactiontube 2 at lower temperatures.

Preferably the cleaning gas contains nitrogen gas as a diluent gas. Dueto the dilution of the cleaning gas with nitrogen gas, the duration ofthe cleaning process can be easily set. A cleaning gas not containingnitrogen gas is highly reactive. Therefore, the duration of the cleaningprocess must precisely be determined with difficulty if a cleaning gasnot containing nitrogen gas is to be used. The dilution of the cleaninggas with nitrogen gas is economically advantageous.

EXAMPLES 2 TO 5

In thin film deposition apparatus cleaning methods in Examples 2 to 5,cleaning gases containing HF gas are used as an additive gas. Etch ratesand selectivities in Examples 2 to 5 were determined by a method similarto that of Example 1. In a thin film deposition apparatus cleaningmethod in Example 2, fluorine gas, hydrogen fluoride gas and nitrogengas at 1.5 l/min, 0.5 l/min and 8 l/min were supplied respectively. Thatis to say a cleaning gas at 10 l/min in total into the inner tube 3heated at 300° C. and maintained at a pressure of 53,200 Pa (400 torr).In the thin film deposition apparatus cleaning methods in Examples 3 to5, cleaning gases having fluorine gas concentrations and hydrogenfluoride concentrations different from those of the cleaning gas used inExample 2 were used. In a thin film deposition apparatus cleaning methodin Comparative example 3, a cleaning gas containing hydrogen fluoridegas and nitrogen gas was used and the reaction tube 2 was heated at 300°C. In a thin film deposition apparatus cleaning method in Comparativeexample 4, fluorine gas, hydrogen fluoride gas and nitrogen gas weresupplied at 1 l/min, 1 l/min and 8 l/min, respectively. That is to say,cleaning gas was supplied in total at 10 l/min into the reaction tube 2heated at 400° C. FIGS. 6 to 8 show measured results.

It is obviously known, from the comparative examination of data on theresult of cleaning in Comparative example 1 using the cleaning gas notcontaining hydrogen fluoride gas shown in FIGS. 3 and 4, and data shownin FIGS. 6, 7 and 8, that the cleaning gas containing hydrogen fluoridegas is capable of etching silicon nitride at a high etch rate and hashigh Si₃N₄ selectivities with respect to quartz and SiC. The cleaninggas containing hydrogen fluoride gas, similarly to the cleaning gascontaining chlorine gas, is capable of removing silicon nitride adheringto the inner surfaces of the reaction tube without deteriorating thereaction tube 2 and the jigs.

It is known from data on the result of cleaning by Examples 2 to 4 thatit is preferable to supply the cleaning gas into the inner tube 3 sothat the flow rate ratio between fluorine gas and hydrogen fluoride gasis in the range of 1:3 to 3:1. A cleaning gas having such fluorine gasand hydrogen fluoride gas concentrations is capable of etching siliconnitride at a high etch rate.

Particularly, the cleaning gas used in Example 3 and supplied so thatthe flow rate ratio between fluorine gas and hydrogen fluoride gas is1:1, can further increase silicon nitride etch rate and further decreasequartz etch rate. Consequently, the Si₃N₄ selectivity with respect toquartz can further be increased, and hence silicon nitride adhering tothe inner surfaces of the reaction tube 2 can be removed withoutdeteriorating the reaction tube 2 and the jigs.

As is apparent from data on the result of cleaning by Example 5, siliconnitride etch rate can further be increased and quartz etch rate canfurther be decreased when fluorine gas and hydrogen fluoride gas aresupplied at an increase flow rate of 2 l/min. Thus, it is preferable toincrease the respective flow rates of fluorine gas and hydrogen fluoridegas, while maintaining the flow rate ratio between fluorine gas andhydrogen fluoride gas at 1:1.

As is apparent from data on the result of cleaning by Example 3 andComparative example 4, although silicon nitride etch rate increases whenthe temperature of the reaction tube 2 is raised from 300° C. to 400°C., quartz etch rate and SiC etch rate increases greatly and,consequently, Si₃N₄ selectivity decreases. Thus, it was proved that itis preferable that in the cleaning process, similarly to the cleaningprocess using the cleaning gas containing chlorine gas, the interior ofthe reaction tube 2 was at 300° C. lower than 400° C. and a cleaning gascontaining hydrogen fluoride gas was used to enhance silicon nitrideetch rate without decreasing Si₃N₄ selectivity (maintaining Si₃N₄selectivity at a high level). It is preferable that in the cleaning stepusing the cleaning gas containing hydrogen fluoride gas, similarly tothe cleaning step using the cleaning gas containing chlorine gas, heatsthe interior of the reaction tube 2 was heated, for the cleaning step,at temperatures below 400° C. More preferably, the temperature in thereaction tube for the cleaning step is in the range of 250° C. to 380°C.

EXAMPLES 6 TO 8

In thin film deposition apparatus cleaning methods in Examples 6 to 8,cleaning gases containing ammonia gas were used as an additive gas. Etchrates and selectivities in by Examples 6 to 8 were determined by amethod similar to that in Example 1. In a thin film deposition apparatuscleaning method in Example 6, fluorine gas, ammonia gas and nitrogen gasat 1.78 l/min, 0.17 l/min and 8.05 l/min were supplied, respectively.That is to say, a cleaning gas was supplied in total at 10 l/min intothe inner tube 3 heated at 300° C. and maintained at a pressure of53,200 Pa (400 torr). In thin film deposition apparatus cleaning methodsin Examples 7 and 8, cleaning gases having fluorine gas concentrationsand ammonia gas concentrations different from those of the cleaning gasused in Example 6 were used. Measured data on the result of cleaning byExamples 6 to 8 is shown in FIGS. 9 to 11.

It is obviously known, from the comparative examination of data on theresult of cleaning in Comparative example 1 using the cleaning gas notcontaining ammonia gas shown in FIGS. 3 and 4, and data shown in FIGS. 9and 10, that the cleaning gas containing ammonia gas is capable ofetching silicon nitride at a high etch rate and has high Si₃N₄selectivities with respect to quartz and SiC as shown in FIGS. 9 and 11.The cleaning gas containing ammonia gas, similarly to the cleaning gascontaining chlorine gas, is capable of removing silicon nitride adheringto the inner surfaces of the reaction tube 2 without deteriorating thereaction tube 2 and the jigs.

It is preferable to supply the cleaning gas into the inner tube 3 likeExamples 6 to 8, such that the flow rate ratio between fluorine gas andammonia gas is in the range of 2:1 and 10:1. Such a cleaning gas iscapable of etching silicon nitride at a high etch rate. It is morepreferable to supply the cleaning gas into the inner tube 3 such thatthe flow rate ratio between fluorine gas and ammonia gas is in the rangeof 3:1 and 7:1. Particularly, the cleaning gas supplied such that theflow rate ratio between fluorine gas and ammonia gas in carrying outExample 7 is about 4.5:1, can increases silicon nitride etch, anddecrease quartz etch rate. Thus, silicon nitride selectivity withrespect to quartz can be increased. Consequently, silicon nitrideadhering to the inner surfaces of the reaction tube 2 can be removedwithout deteriorating the reaction tube 2 and the like.

EXAMPLES 9 TO 11

In thin film deposition apparatus cleaning methods in Examples 9 to 11,cleaning gases containing hydrogen gas were used as an additive gas.Etch rates and selectivities in Examples 9 to 11 were determined by amethod similar to that of Example 1. In a thin film deposition apparatuscleaning method in Example 9,fluorine gas, hydrogen gas and nitrogen gasat 1.78 l/min, 0.37 l/min and 8 l/min were supplied respectively. Thatis to say, a cleaning gas was in total supplied at 10.12 l/min into theinner tube 3 heated at 300° C. and maintained at a pressure of 53,200 Pa(400 torr). In thin film deposition apparatus cleaning methods inExamples 10 and 11, cleaning gases having fluorine gas concentrationsand hydrogen gas concentrations different from those of the cleaning gasused in Example 9 were used. Measured data on the result of cleaning inExamples 9 to 11 is shown in FIGS. 12 to 14.

It is obviously known, from the comparative examination of data on theresult of cleaning in Comparative example 1 using the cleaning gas notcontaining hydrogen gas shown in FIGS. 3 and 4, and data shown in FIGS.12 and 13, that the cleaning gas containing hydrogen gas is capable ofetching silicon nitride at a high etch rate and has high Si₃N₄selectivities with respect to quartz and SiC as shown in FIGS. 12 and14. The cleaning gas containing hydrogen gas, similarly to the cleaninggas containing chlorine gas, is capable of removing silicon nitrideadhering to the inner surfaces of the reaction tube 2 withoutdeteriorating the reaction tube 2 and the jigs.

It is preferable to supply the cleaning gas into the inner tube 3 likeExamples 9 to 11, such that the flow rate ratio between fluorine gas andhydrogen gas is in the range of 5:1 and 5:3. Such a cleaning gas iscapable of etching silicon nitride at a high etch rate. It was verifiedthat the silicon nitride etching effect of the cleaning gas does notchange significantly even if the flow rate ratio between fluorine gasand hydrogen gas changes in the range of 5:1 and 5:3. Therefore, highsilicon nitride etch rate can be achieved even if the flow rate ofhydrogen is not controlled precisely. Thus, the use of hydrogen gas asan additive gas can facilitate the control of the flow rate of theadditive gas.

Quartz etch rate does not increase even if the flow rate of hydrogen gasis increase so that the flow rate ratio between fluorine gas andhydrogen gas is 5:3 (Example 11). Consequently, the Si₃N₄ selectivitywith respect to quartz can further be increased and silicon nitrideadhering to the inner surfaces of the reaction tube 2 can be removedwithout deteriorating the reaction tube 2 and the like.

As is apparent from the foregoing description, according to the presentinvention, the cleaning gas containing the additive gas is capable ofetching silicon nitride at a high etch rate without heating the reactiontube 2 at an elevated temperature. Since the Si₃N₄ selectivity does notdecrease when the cleaning gas containing the additive gas is used, andhence the reaction tube and the jigs are not deteriorated easily.Consequently, silicon nitride adhering to the inner surfaces of thethermal processing apparatus can be removed without deteriorating thereaction tube 2 and the jigs.

According to the present invention, the cleaning gas containing theadditive gas is capable of etching silicon nitride at a high etch rate,and hence the reaction tube 2 may be heated at a comparatively lowtemperature for the cleaning step, which further reduces thedeteriorating effect of the cleaning step on the reaction tube 2 and thejigs.

According to the present invention, the cleaning gas containing nitrogengas as a diluent can facilitate setting a cleaning time for the cleaningprocess.

The present invention is not limited in its practical application to theforegoing embodiments, and various modifications of the foregoingembodiments and applications of those are possible. Modificationsaccording to the present invention will be described.

The cleaning gas may contain any type of gas as an additive gas,provided that the additive gas is capable of promoting the activation offluorine gas. Such a cleaning gas etches silicon nitride at a high etchrate. The cleaning gas may contain any type of additive gas, providedthat the cleaning gas is capable of etching silicon nitride at a highetch rate without decreasing Si₃N₄ selectivity with respect to materialsforming the internal members of the thermal processing apparatus 1, suchas quartz and SiC. The reaction tube 2 and the jigs are not deterioratedsignificantly when the cleaning gas has a high Si₃N₄ selectivity. Theadditive gas may be a halogen gas, such as bromine gas (Br₂) instead ofchlorine gas, hydrogen fluoride gas, ammonia gas or hydrogen gas.

Although the invention has been described as applied to removing siliconnitride deposited on the inner surfaces of the thermal processingapparatus 1, the present invention is applicable to removing depositsother than the silicon nitride deposit; the present invention can beapplied to removing, for example, polysilicon, titanium oxide, tantalumoxide, silica, silicone-germanium (SiGe), BSTO (BaSrTiO₃) and STO(SrTiO₃). The deposit is not necessarily a reaction product, and may bea reaction byproduct, such as ammonium chloride.

When the reaction product, such as silicon nitride, and a reactionbyproduct, such as ammonium chloride or a Si—Cl—N—H compound, depositedparticularly on the inner surface of the exhaust pipe 17 of the thermalprocessing apparatus 1, those deposits can effectively be removed withthe cleaning gas containing fluorine gas and the additive gas thatpromotes the activation of fluorine gas.

To remove the deposits deposited on the inner surface of the exhaustpipe 17, the cleaning gas is supplied through the reaction tube 2 intothe exhaust pipe 17. The cleaning gas may be supplied through an inletport 17 a formed in the exhaust pipe 17 into the exhaust pipe 17. Thedeposits deposited on the inner surface of the exhaust pipe 17 caneffectively removed by heating the exhaust pipe 17 with an exhaust pipeheater 17 b.

Although the foregoing embodiments of the present invention use thecleaning gases containing nitrogen gas as the diluent gas, the cleaninggases do not necessarily need to contain the diluent gas. However, it ispreferable to use a cleaning gas containing a diluent gas because thecleaning gas containing the diluent gas facilitates setting a cleaningtime for the cleaning process. Preferably, the diluent gas is an inertgas. For example, helium gas (He), neon gas (Ne) or argon gas (Ar) maybe used instead of nitrogen gas.

Although the foregoing embodiments of the present invention sets thepressure in the reaction tube 3 at 53,200 Pa (400 torr) to clean theinterior of the thermal processing apparatus 1, the pressure in thereaction tube 3 is not limited thereto. The cleaning of the thermalprocessing apparatus 1 may be carried out once every several cycles ofthe film deposition process or once every one cycle of the filmdeposition process. The life of the internal components formed of quartzand SiC of the thermal processing apparatus 1 can further be extended bycleaning the interior of the thermal processing apparatus once every onecycle of the film deposition process.

Although the invention has been described as applied to cleaning thebatch-furnace vertical thermal processing apparatus provided with thedouble-wall reaction tube 2 consisting of the inner tube 3 and the outertube 4, the present invention is not limited thereto in its practicalapplication. For example, the present invention is applicable tocleaning a batch-furnace thermal processing apparatus provided with areaction tube not having any tube corresponding to the inner tube 3. Theworkpieces are not limited to semiconductor wafers 10, and may be, forexample, glass substrates for LCDs.

As is apparent from the foregoing description, according to the presentinvention, the deposits deposited in the thermal processing apparatuscan be removed without significantly deteriorating the reaction vesseland the jigs.

1. A thin film deposition apparatus cleaning method of cleaning a thinfilm deposition apparatus by removing deposits adhering to an innersurfaces of the thin film deposition apparatus after depositing thinfilms on workpieces by supplying a process gas into a reaction vesselincluded in the thin film deposition apparatus, said thin filmdeposition apparatus cleaning method comprising the steps of: heating aninterior of the reaction vessel at a predetermined temperature; andcleaning an interior of the thin film deposition apparatus by supplyinga cleaning gas containing fluorine gas and an additive gas capable ofpromoting the activation of the fluorine gas into the reaction vesselheated at the predetermined temperature, heating the cleaning gas at apredetermined temperature to activate the fluorine gas contained in thecleaning gas, and removing the deposits with the activated fluorine gas.2. The thin film deposition apparatus cleaning method according to claim1, wherein the deposits are removed and the interior of the thin filmdeposition apparatus is cleaned by supplying the cleaning gas containingfluorine gas and the additive gas capable of promoting the activation ofthe fluorine gas and of increasing etch rate for the deposits withoutdecreasing selectivity with respect to the materials forming theinternal members of the thin film deposition apparatus, into thereaction vessel in the cleaning step.
 3. The thin film depositionapparatus cleaning method according to claim 2, wherein the additive gasis chlorine gas, hydrogen fluoride gas, ammonia gas or hydrogen gas. 4.The thin film deposition apparatus cleaning method according to claim 3,wherein the deposits are removed to clean the interior of the thin filmdeposition apparatus by supplying a cleaning gas containing fluorine gasand chlorine gas into the reaction vessel heated at the predeterminedtemperature in the cleaning step.
 5. The thin film deposition apparatuscleaning method according to claim 3, wherein the deposits are removedto clean the interior of the thin film deposition apparatus by supplyinga cleaning gas containing fluorine gas and hydrogen fluoride gas intothe reaction vessel heated at a predetermined temperature in thecleaning step.
 6. The thin film deposition apparatus cleaning methodaccording to claim 3 or 5, wherein the cleaning gas containing fluorinegas and hydrogen fluoride gas is supplied such that the flow rate ratiobetween fluorine gas and hydrogen fluoride gas is in the range of 1:3 to3:1.
 7. The thin film deposition apparatus cleaning method according toclaim 6, wherein the cleaning gas containing fluorine gas and hydrogenfluoride gas is supplied such that the flow rate ratio between fluorinegas and hydrogen fluoride gas is 1:1.
 8. The thin film depositionapparatus cleaning method according to claim 7, wherein fluorine gas andhydrogen fluoride gas are supplied at a flow rates not lower than 2l/min respectively.
 9. The thin film deposition apparatus cleaningmethod according to claim 3, wherein the deposits are removed to cleanthe interior of the thin film deposition apparatus by supplying acleaning gas containing fluorine gas and ammonia gas into the reactionvessel heated at a predetermined temperature in the cleaning step. 10.The thin film deposition apparatus cleaning method according to claim 9,wherein the cleaning gas containing fluorine gas and ammonia gas issupplied such that the flow rate ratio between fluorine gas and ammoniagas is in the range of 2:1 to 10:1.
 11. The thin film depositionapparatus cleaning method according to claim 3, wherein the deposits areremoved to clean the interior of the thin film deposition apparatus bysupplying a cleaning gas containing fluorine gas and hydrogen gas intothe reaction vessel heated at a predetermined temperature in thecleaning step.
 12. The thin film deposition apparatus cleaning methodaccording to claim 11, wherein the cleaning gas containing fluorine gasand hydrogen gas is supplied such that the flow rate ratio betweenfluorine gas and hydrogen gas is in the range of 5:1 to 5:3.
 13. Thethin film deposition apparatus cleaning method according to claim 12,wherein the cleaning gas containing fluorine gas and hydrogen gas issupplied such that the flow rate ratio between fluorine gas and hydrogengas is 5:3.
 14. The thin film deposition apparatus cleaning methodaccording to claim 1, wherein internal members of the thin filmdeposition apparatus are formed of at least either quartz or siliconcarbide.
 15. The thin film deposition apparatus cleaning methodaccording to claim 1, wherein the interior of the reaction vessel isheated at a temperature below 400° C. in the heating step.
 16. The thinfilm deposition apparatus cleaning method according to claim 15, whereinthe interior of the reaction vessel is heated at a temperature in therange of 250° C. to 380° C. in the heating step.
 17. The thin filmdeposition apparatus cleaning method according to claim 1, wherein thecleaning gas is diluted with a diluent gas to produce a diluted cleaninggas, and the diluted cleaning gas is supplied into the reaction vessel.18. The thin film deposition apparatus cleaning method according toclaim 17, wherein the diluent gas is an inert gas.
 19. The thin filmdeposition apparatus cleaning method according to claim 1, wherein thinfilms formed on the workpieces are silicon nitride films, and thesilicon nitride deposited in the thin film deposition apparatus isremoved in the cleaning step, when depositing the silicon nitride filmson the workpieces with the cleaning gas.
 20. A thin film depositionapparatus cleaning method of cleaning a thin film deposition apparatusby removing deposits adhering to the inner surface of an exhaust pipeafter forming thin films on workpieces by supplying a process gas into areaction vessel included in the thin film deposition apparatus, anddischarging gases from the reaction vessel into the exhaust pipe, saidthin film deposition apparatus cleaning method comprising the steps:heating an interior of the exhaust pipe at a predetermined temperature;and cleaning an interior of the exhaust pipe by supplying a cleaning gascontaining fluorine gas, and an additive gas capable of promoting theactivation of the fluorine gas into the exhaust pipe heated at thepredetermined temperature in the heating step, heating the cleaning gasat a predetermined temperature to activate the fluorine gas contained inthe cleaning gas, and removing the deposits with the activated fluorinegas.
 21. The thin film deposition apparatus cleaning method according toclaim 20 wherein the cleaning gas is supplied through the reactionvessel into the exhaust pipe.
 22. The thin film deposition apparatuscleaning method according to claim 20, wherein the cleaning gas issupplied through an inlet port formed in the exhaust pipe into theexhaust pipe.